0 – 24 Volt, 2 Amp Bench Top Power Supply

Hobbyist electronics projects need robust, reliable power supplies for prototyping and testing. I learned how to build this circuit from the Basic Analog Circuits class at ITP taught by Eric Rosenthal, but took it several steps further in building a solid enclosure and integrating a voltage meter. Now it lives on my desk, ready to power most small projects I’m working on.

You’ll see example shots of point-to-point wiring of components to perfboard while following a schematic for this power supply. A wood enclosure is built, and Adafruit’s Mini Volt Meter, Vout posts, and a potentiometer are mounted in the final product.

Parts List:

  • One 3×5″ perfboard
  • LM317 variable voltage regulator
  • BR805D Bridge Rectifier
  • Heat Sink
  • 120 VAC to 24 VDC transformer (mine is part number LP-575)
  • Power cable
  • Two 1000 microfarad capacitors
  • One 0.1 microfarad capacitor
  • One 1 microfarad capacitor
  • One 100 ohm resistor
  • One 5k ohm variable resistor
  • One 1N4002 diode
  • 1/2″ plywood
  • 1/8″ wood or MDF
  • six half inch wood screws
  • 8 1/2″ long x 1/8″ wide nuts and bolts
  • Plastic knob
  • Mini volt meter from Adafruit Industries



Step #1:

0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply
  • Solder the positive and negative (red and black) leads from the transformer to the power cable. Twist the threaded wires together and use a liberal amount of solder, completely covering all connections. Finish with heat shrink tubing or electrical tape.
  • Apply thermal compound to LM317 and screw into heat sink.
  • Wire all components to the perfboard. There are a couple of ways to go about this: some find it's easier to put all the components into the holes first and bend the wires so they stay in place, then solder everything together. I like to go step by step, following each part of the schematic individually to verify that I have every connection correct.
  • You'll be using point-to-point wiring on the back of the perfboard. Make sure that all your connections are separated, and use insulated wires if you have to cross over any connections you've already made.
  • Make sure to solder leads onto your potentiometer for easy mounting to the enclosure later on. Also be sure to short out the middle pin to an adjacent pin on the pot, so it functions as a variable resistor and not a voltage divider.
  • Solder long leads to two header pins on your positive and negative output for easy mounting to the enclosure later on.

Step #2:

0 – 24 Volt, 2 Amp Bench Top Power Supply
  • Solder the mini volt meter directly to the output leads.
  • Now you should be ready to test your power supply. Remember that you are working with high voltage from the mains. Use all proper precautions when testing, and if you don't know what those are, find someone who does and can help you!
  • Be ready to unplug quickly if you see smoke or smell something funny. Usually this might happen because a component is shorted and burned out. It can generally be diagnosed and fixed relatively quickly.

Step #3:

0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply
  • There are many different ways to build wooden boxes for project enclosures. Briefly, I used the thick plywood as a base to drill into, and attached the thinner sidewalls with machine screws after drilling pilot holes. I then hot-glued the sides and top together.
  • I used a 1" hole saw to snake the power cable through. This leaves room for the plug to fit through and also aids in ventilation.
  • Attach the perfboard and transformer to the bottom of the enclosure using nuts and bolts.

Step #4:

0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply
  • Drill holes for your potentiometer and power terminals, and cut a space for your volt meter. I used a laser cutter to do this step, but it can also be done with a drill and a coping saw or scroll saw.
  • Twist the positive and negative leads to two separate screws. These will serve as your power terminals.
  • Attach power terminals and potentiometer to the face of the enclosure using nuts.
  • The mini volt meter comes with mounting holes, but I opted to hot glue it into place. This seemed to secure it well.

Step #5:

0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply0 – 24 Volt, 2 Amp Bench Top Power Supply
  • Carefully tuck all your wires into the enclosure and hot glue the control panel to the rest of the enclosure.
  • Attach a knob to your potentiometer.
  • Make sure you've clearly labelled your positive and negative terminals. Now you can easily attach alligator clips to them and use this adjustable power supply for many different types of electronics projects.
Michael Colombo

Michael Colombo

In addition to being an online editor for MAKE Magazine, Michael Colombo works in fabrication, electronics, sound design, music production and performance (Yes. All that.) In the past he has also been a childrens' educator and entertainer, and holds a Masters degree from NYU's Interactive Telecommunications Program.

  • Colombo

    It was supplied by my institution, probably bought in bulk. But you can use any transformer that has similar specs – judging from a recent user comment you’d probably want to go with one that’s lower amperage so you don’t accidentally burn out the LM317.

  • Colombo

    Sorry I’m not exactly sure what you mean…did you find different part numbers from JameCo? What do you wish to edit?

  • Colombo

    I think you could test it with a 9 volt to see if the LM317 is doing its job – though someone may need to verify this for me…

  • Joseph

    I mean just adding links to Jameco products
    (Note I am not affiliated with Jameco. I just opened their catalog first.)

  • Joseph

    This should be fine, BUT you will not be able to get a full 24v.
    Just 1.5v-9v about.

  • Colombo

    Great to hear you’ve improved upon the original design! Once you’re finished please post links to photos, or put them in the Makezine flickr pool.

    – The best place for a fuse is probably right after the bridge rectifier on the positive lead, before it goes through the rest of the circuit.

  • Eric Marcoullier

    Did you ever find the Jameco part numbers? I can’t find a suitable transformer but I’m not sure if I’m looking correctly :)

  • pranker225

    go here:

  • Doug Strickland

    @John – You can still use the transformer mentioned in the project (Jameco Part no. 112513) because it is rated for both primary voltages. Here’s from the datasheet:

    Primary Voltage: 115/230VAC @ 50-60Hz
    Secondary Voltage: 24VAC @ 2A

  • Andrew wiles

    Used these schematics but changed lm317 for lm338 and now i have a 1.5 to 35v 0-3.5a power supply great just finished it and very chuffed with it

    • Alberto

      If I read it right you have current and voltage regulation? can you post pictures or schematics?

  • Jasonc

    I didn’t see the bridge rectifier used in any of the steps…

  • Aman Singhal

    CAN i really rely on this i mean does it really work

  • Aman Singhal

    bro it does not work this power supply is rubbish

  • Matthew Lindner

    Just to clarify, this will not do 0 volts due to the ref voltage of the LM317. The lowest you can go is 1.25 with this regulator. Additionally it is only rated at 1.5A max current.

  • Bo Maryniuk

    I just assembled this with my own designed PCB and used 4 diodes SB260 for the rectifier and ring transformer 230V – 2x24V. Four things I would like to highlight:
    1. While transformer output is stable 26.4, it somewhat outputs me 33.7V at max.
    2. Potentiometer just that sucks: one human hair width turn and you have 15V instead of 12V. Meh… It is better to use step switch with trimmers and setup 5-6 presets, like 1.5V, 3.3V, 5V, 6V, 9V, 12V, 24V instead.
    3. Yes, it gives me 1.27V at minimum, not 0V as advertised.
    4. You *need* heat sink for the regulator!

    Hope this helps.

    • 2. A nice 10-turn pot would solve that nicely though, don’t you think?
      4. I do believe that’s mentioned in the schematic, but it bears repeating none the less.

      • Bo Maryniuk

        It is exactly what I just did :)

        Additionally, I found current is jumping. :( I have no idea why. The output gets higher or lower almost within the range of 1V.

    • 1. The transformer outputs 24VAC. You cannot compare 24VAC to 24VDC directly. So, the 24VAC from the transformer is called ‘Vrms’ (google it). Basically, you can get the DC equivalent by multiplying the Vrms by the square root of 2, which is about 1.41. 24 x 1.41 = 33.8V DC.

      3. True, the LM317 has an 1.25V offset. You can work around this, but it gets complicated fast.

      • Bo Maryniuk

        Cool, many thanks!

  • dominic garcia

    I am curious how you decided on the capacitors for this circuit and what role they play? Does it have to do with the ripple?

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  • >0 – 24 Volt, 2 Amp

    Hi Michael,

    I don’t think that this circuit can provide 2A, at least not on all ranges of its output voltage.

    An example. Let’s say that we set the output voltage to 2V. The input voltage for LM317 here is around 24V, so the difference between “in” and “out” pins would be 22V. If we would want to get 2A in this case, then this current would flow as well between mentioned pins. That gives us 22V*2A=48W of power turned into heat, such radiator as used here can’t dissipate it.


  • Crimsonfire

    I tried this in simulator but my voltage AC source is 220 Vac. The lowest output I can get was at the picture. How can I lower this to 1 V? Are there any materials I need to add?